11.4.2 Drawing functions

The scan-line conversions of the drawing functions are very much host-dependent. In other words, you cannot assume that, for example
(draw-point port x y)
has exactly the same effect on all machines. Some machines might put pixels down and to the right of integer coordinates
(x y)
while others may center the pixel at
(x y)
.

See also the LispWorks
CAPI Reference Manual
entries for
draw-circle
(which draws a circle) and
draw-ellipse
(which draws an ellipse) and other drawing functions.